Twist drill

A twist drill comprising:

• a cylindrical body including:
• an axis of rotation therethrough,
• a forward end which contacts a workpiece,
• a spiral flute formed in an outer peripheral surface of said body so as to extend spirally along a length thereof to said forward end and a land disposed adjacent to said flute, said flute having
• a first wall facing in a direction of rotation of said body and a second wall extending from an inner end of said first wall to the outer periphery of said body, said first wall terminating at said forward end in a first cutting lip having a radially outermost end disposed on the outer periphery of said body, said second wall being concavely shaped when viewed from said forward end and formed so that, assuming a first line extending from said outermost end perpendicular to a second line connecting said outermost end and said axis of said body, the maximum distance between said first line and second wall is set in a range from 0.45 D to 0.65 D, wherein D is a diameter of said body,
• said body being made of a material selected from the group consisting of high speed steel and sintered metal high speed steel,
• said body having a web thickness of 0.15 D to 0.3 D,
• at least said forward end of said body being coated with a hard coating which is harder than said body,
• said body has a flute-width ratio of 0.4 to 0.9, and
• wherein a web portion of the drill is ground off to provide a second cutting lip extending away from the axis of said body, each of first and second cutting lips being formed to be linear as viewed from said forward end
• wherein that corner at which said first cutting lip and said second cutting lip meet forms a generally arcuately shaped edge when viewed from said forward end.

A twist drill comprising:

• a cylindrical body including:
• an axis of rotation therethrough,
• a forward end which contacts a workpiece,
• a spiral flute formed in an outer peripheral surface of said body so as to extend spirally along a length thereof to said forward end and a land disposed adjacent to said flute, said flute having
• a first wall facing in a direction of rotation of said body and a second wall extending from an inner end of said first wall to the outer periphery of said body, said first wall terminating at said forward end in a first cutting lip having a radially outermost end disposed on the outer periphery of said body, said second wall being concavely shaped when viewed from said forward end and formed so that, assuming a first line extending from said outermost end perpendicular to a second line connecting said outermost end and said axis of said body, the maximum distance between said first line and second wall is set in a range from 0.45 D and 0.65 D, wherein D is a diameter of said body,
• said body being made of a material selected from the group consisting of high speed steel and sintered metal high speed steel,
• said body having a web thickness of 0.15 D to 0.3 D,
• at least said forward end of said body being coated with a hard coating which is harder than said body,
• the ratio of arc length of said flute to arc length of said land at a cross-section taken perpendicular to the axis of said body being 0.9 to 1.2,
• said first wall having an arcuately shaped portion which contacts an imaginary cylinder inscribing a web portion of the drill, and
• said arcuately shaped portion having a radius of curvature of between 0.15 D and 0.2 D,
• in which a web portion of the drill is ground off to provide a second cutting lip extending away from the axis of said body, each of first and second cutting lips being formed to be linear as viewed from said forward end,
• in which said first cutting lip has a radial rake angle of -10.degree. to -20.degree. at said outermost end,
• in which, when a point P is defined by the intersection of a line tangential to said first cutting lip with a line tangential to said second cutting lip, the ratio of a distance between said axis of said body and said point P to a distance between said outermost end of said first cutting lip and said point P is set to range between 0.4:1 and 0.7:1.

A twist drill comprising:

• a cylindrical body including:
• an axis of rotation therethrough,
• a forward end which contacts a workpiece,
• a spiral flute formed in an outer peripheral surface of said body so as to extend spirally along a length thereof to said forward end and a land disposed adjacent to said flute, said flute having
• a first wall facing in a direction of rotation of said body and a second wall extending from an inner end of said first wall to the outer periphery of said body, said first wall terminating at said forward end in a first cutting lip having a radially outermost end disposed on the outer periphery of said body, said second wall being concavely shaped when viewed from said forward end and formed so that, assuming a first line extending from said outermost end perpendicular to a second line connecting said outermost end and said axis of said body, the maximum distance between said first line and second wall is set in a range from 0.45 D and 0.65 D, wherein D is a diameter of said body,
• said body being made of a material selected from the group consisting of high speed steel and sintered metal high speed steel,
• said body having a web thickness of 0.15 D to 0.3 D,
• at least said forward end of said body being coated with a hard coating which is harder than said body,
• the ratio of arc length of said flute to arc length of said land at a cross-section taken perpendicular to the axis of said body being 0.9 to 1.2,
• said first wall having an arcuately shaped portion which contacts an imaginary cylinder inscribing a web portion of the drill, and
• said arcuately shaped portion having a radius of curvature of between 0.15 D and 0.2 D,
• in which a web portion of the drill is ground off to provide a second cutting lip extending away from the axis of said body, each of first and second cutting lips being formed to be linear as viewed from said forward end,
• in which said second cutting lip is inclined at an angle of 15.degree. to 35.degree. with respect to the line extending from the axis of said body to said outermost end of said first cutting lip,
• in which a pair of said first cutting lips and a pair of said second cutting lips are provided, and in which, assuming a first imaginary line extending from an inner ridgeline of one of said second cutting lips and a second imaginary line extending from an inner ridgeline of the other second cutting lip, an intervening distance between said first and second imaginary lines is set to range between 0.0 to 0.3 mm, said second cutting lips defining a chisel edge therebetween.

A twist drill comprising:

• a cylindrical body including:
• an axis of rotation therethrough,
• a forward end which contacts a workpiece,
• a spiral flute formed in an outer peripheral surface of said body so as to extend spirally along a length thereof to said forward end and a land disposed adjacent to said flute, said flute having
• a first wall facing in a direction of rotation of said body and a second wall extending from an inner end of said first wall to the outer periphery of said body, said first wall terminating at said forward end in a first cutting lip having a radially outermost end disposed on the outer periphery of said body, said second wall being concavely shaped when viewed from said forward end and formed so that, assuming a first line extending from said outermost end perpendicular to a second line connecting said outermost end and said axis of said body, the maximum distance between said first line and second wall is set in a range from 0.45 D and 0.65 D, wherein D is a diameter of said body,
• said body being made of a material selected from the group consisting of high speed steel and sintered metal high speed steel,
• said body having a web thickness of 0.15 D to 0.3 D,
• at least said forward end of said body being coated with a hard coating which is harder than said body,
• the ratio of arc length of said flute to arc length of said land at a cross-section taken perpendicular to the axis of said body being 0.9 to 1.2,
• said first wall having an arcuately shaped portion which contacts an imaginary cylinder inscribing a web portion of the drill, and
• said arcuately shaped portion having a radius of curvature of between 0.15 D and 0.2 D,
• in which a web portion of the drill is ground off to provide a second cutting lip extending away from the axis of said body, each of first and second cutting lips being formed to be linear as viewed from said forward end,
• in which that corner at which said first cutting lip and said second cutting lip meet forms a generally arcuately shaped edge when viewed from said forward end,
• in which the radius of curvature of said arcuately shaped edge is between 0.05 D and 0.15 D.

A twist drill comprising:

• a cylindrical body including:
• an axis of rotation therethrough,
• a forward end which contacts a workpiece,
• a spiral flute formed in an outer peripheral surface of said body so as to extend spirally along a length thereof to said forward end and a land disposed adjacent to said flute, said flute having
• a first wall facing in a direction of rotation of said body and a second wall extending from an inner end of said first wall to the outer periphery of said body, said first wall terminating at said forward end in a first cutting lip having a radially outermost end disposed on the outer periphery of said body, said second wall being concavely shaped when viewed from said forward end and formed so that, assuming a first line extending from said outermost end perpendicular to a second line connecting said outermost end and said axis of said body, the maximum distance between said first line and second wall is set in a range from 0.45 D to 0.65 D, wherein D is a diameter of said body,
• said body being made of a material selected from the group consisting of high speed steel and sintered metal high speed steel,
• said body having a web thickness of 0.15 D to 0.3 D,
• at least said forward end of said body being coated with a hard coating which is harder than said body,
• said body has a flute-width ratio of 0.4 to 0.9, and
• wherein a web portion of the drill is ground off to provide a second cutting lip extending away from the axis of said body, each of first and second cutting lips being formed to be linear as viewed from said forward end, and
• wherein said second cutting lip is inclined at an angle of 15.degree. to 35.degree. with respect to the line extending from the axis of said body to said outermost end of said first cutting lip.

A twist drill comprising:

• a cylindrical body including:
• an axis of rotation therethrough,
• a forward end which contacts a workpiece,
• a spiral flute formed in an outer peripheral surface of said body so as to extend spirally along a length thereof to said forward end and a land disposed adjacent to said flute, said flute having
• a first wall facing in a direction of rotation of said body and a second wall extending from an inner end of said first wall to the outer periphery of said body, said first wall terminating at said forward end in a first cutting lip having a radially outermost end disposed on the outer periphery of said body, said second wall being concavely shaped when viewed from said forward end and formed so that, assuming a first line extending from said outermost end perpendicular to a second line connecting said outermost end and said axis of said body, the maximum distance between said first line and second wall is set in a range from 0.45 D to 0.65 D, wherein D is a diameter of said body,
• said body being made of a material selected from the group consisting of high speed steel and sintered metal high speed steel,
• said body having a web thickness of 0.15 D to 0.3 D,
• at least said forward end of said body being coated with a hard coating which is harder than said body,
• said body has a flute-width ratio of 0.4 to 0.9, and
• wherein a web portion of the drill is ground off to provide a second cutting lip extending away from the axis of said body, each of first and second cutting lips being formed to be linear as viewed from said forward end, and
• wherein at least said forward end of said body is coated with a hard coating.

A twist drill comprising:

• a cylindrical body including:
• an axis of rotation therethrough,
• a forward end which contacts a workpiece,
• a spiral flute formed in an outer peripheral surface of said body so as to extend spirally along a length thereof to said forward end and a land disposed adjacent to said flute, said flute having
• a first wall facing in a direction of rotation of said body and a second wall extending from an inner end of said first wall to the outer periphery of said body, said first wall terminating at said forward end in a first cutting lip having a radially outermost end disposed on the outer periphery of said body, said second wall being concavely shaped when viewed from said forward end and formed so that, assuming a first line extending from said outermost end perpendicular to a second line connecting said outermost end and said axis of said body, the maximum distance between said first line and second wall is set in a range from 0.45 D to 0.65 D, wherein D is a diameter of said body,
• said body being made of a material selected from the group consisting of high speed steel and sintered metal high speed steel.
• said body having a web thickness of 0.15 D to 0.3 D,
• at least said forward end of said body being coated with a hard coating which is harder than said body,
• said body has a flute-width ratio of 0.4 to 0.9, and
• wherein a web portion of the drill is ground off to provide a second cutting lip extending away from the axis of said body, each of first and second cutting lips being formed to be linear as viewed from said forward end, and
• wherein when a point P is defined by the intersection of a line tangential to said first cutting lip with a line tangential to said second cutting lip, the ratio of a distance between said axis of said body and said point P to a distance between said outermost end of said first cutting lip and said point P is set to range between 0.4:1 to 0.7:1.